Thermoplastic adhesives, otherwise known as “hot melt” adhesives, have been widely used in industry for various applications. For example, thermoplastic hot melt adhesives are used for carton sealing, case sealing, tray forming, pallet stabilization, nonwoven application including diaper manufacturing, and many other applications. Hot melt adhesive, in its pre-melted state (referred to herein as “particulate” hot melt adhesive), can be provided in a variety of particulate shapes and sizes, ranging from small bb-sized pieces, to larger sized pieces including pellets and chips. Adhesive material, in the form of adhesive particulate, may be stored in an adhesive supply container and transferred to an adhesive melter, as part of an automated filling operation. At the adhesive melter, the adhesive material is then heated and melted to a desired temperature for dispensing. Hot melt adhesives are often dispensed by systems including a dispensing gun coupled via heated hoses to an adhesive melter.
In an automatic fill system, a transfer pump, such as a pneumatic pump, is connected to the adhesive container for transferring the adhesive particulate from the supply container, through a transfer hose, and to the adhesive melter. Pneumatic pumps generally rely on the suction of air located within gaps between individual pieces of adhesive particulate stored within the supply container or air otherwise disposed within the supply container. Traditionally, the adhesive particulate is fed by gravity into a lower portion of the supply container toward an inlet of the transfer pump and covers a majority of the pump inlet. At the start of a traditional fill cycle, the transfer pump generates a vacuum at the pump inlet that withdraws the adhesive particulate and air from the adhesive container. The withdrawn air and adhesive particulate then pass through the transfer hose toward the adhesive melter. In turn, the suction of the air creates a vacuum within the gaps of the adhesive particulate that withdraws additional air from a surrounding environment. The additional air from the surrounding environment continuously replaces the air within the supply container for transferring the adhesive particulate through the transfer pump.
At the end of the traditional fill cycle, the transfer pump is switched off in order to cease the transfer of air and thereby cease the transfer of adhesive particulate. Consequently, adhesive particulate that has already been withdrawn from the supply container into the transfer hose but not yet fully transferred to the adhesive melter collects and is left stranded at various low points and horizontal points within the transfer hose, unable to overcome gravitational forces. These collections of residual adhesive particulate remain within the transfer hose and are later flushed from the hose only by passing additional air through the system at the start of the next fill cycle. This characteristic limits the useful vertical transfer capability of a traditional fill system. In this regard, if a vertical section of the hose is too long, the pressure-limited pump may not be able to lift or push the particulate adhesive material through the vertical hose section during the subsequent fill cycle. Furthermore, some of the horizontal and low points at which stranded adhesive collect are located near heated components. The heat generated by these components may partially or fully melt the stranded adhesive, and lead to adhesive build-up and clogging of the transfer hose. These consequences of stranded adhesive increase the demands on transfer system components, such as the transfer pump, and reduce overall system efficiency.
There is a need, therefore, for an adhesive system and method of use that addresses the present challenges and characteristics such as those discussed above.